1. Field of the Invention
The present invention relates to an imaging system capable of receiving light.
2. Description of the Related Art
A collapsible lens-barrel of a taking lens has been known in which the entire length of the lens-barrel is changeable between a using mode where taking lenses are arranged at shooting intervals and a storing mode where the lens intervals and the space to an image pick-up surface are reduced. Changes in the entire length of the lens-barrel are established by a cam paying-out mechanism and a helicoid paying-out mechanism so as to have an appropriate arrangement of the lens-barrel. Also, a zoom lens-barrel may also be constructed in which a focal length is changed by independently moving two or more lens groups.
FIG. 8 is a lateral sectional view showing a collapsed mode of a conventional collapsible lens-barrel, wherein a CCD 101, which is an imager, includes an imaging surface 101a and a protection glass 101b. A CCD base board 102 retains the CCD 101 and components of the lens-barrel, which will be described later. An optical LPF (low pass filter) 103 prevents a luminance moiré and a false color using birefringence of crystal during shooting an object having a repetition pattern. A first group lens 104 constitutes an optical system of the conventional lens-barrel. Reference numeral 105 denotes a second group lens; and numeral 106 a third group lens in a similar way. In FIG. 8, each group lens is located at a stored position for non-shooting.
FIG. 9 is a lateral sectional view of the lenses shown in FIG. 8 showing a service condition for shooting. A tubular fixed cylinder 107 is fixed to the CCD base board 102. A tubular cam cylinder 108 is provided with a projection formed on the external cylindrical surface so as to be a cam follower. The fixed cylinder 107 is provided with a cam formed inside so as to engage with the cam follower of the cam cylinder 108. The cam cylinder 108 can be rotated by a drive unit (not shown) so as to pay out toward an object while rotating by following the cam of the fixed cylinder 107.
A linear movement cylinder 109 is rotatably fitted with the internal surface of the cam cylinder 108. A claw 109a prevents the linear movement cylinder 109 from coming off the cam cylinder 108. A projection 109b radially extends from the linear movement cylinder 109. A groove 107a is formed on the internal surface of the fixed cylinder 107 in parallel with an optical axis. The projection 109b is fitted with the groove 107a so that the linear movement cylinder 109 is constructed to pay out without rotating by following the rotation paying-out of the cam cylinder 108.
A first group lens-barrel 110 retains the first group lens 104; and a first group cam follower is studded therein and directed outside the first group lens-barrel 110. The first group cam follower moves following a first group cam formed inside the cam cylinder 108. A second group lens-barrel 111 retains the second group lens 105. The second group lens-barrel 111 also has a second group cam follower studded therein and directed outside in the same way as in the first group lens-barrel 110 and moves following a second group cam formed inside the cam cylinder 108.
Furthermore, the linear movement cylinder 109 is provided with a cut-out formed in parallel with the optical axis, and the cut-out is fitted with the first-group cam follower for controlling the first group lens-barrel 110 so as to straight move, so that the first group lens-barrel 110 moves back and forth without rotation along the first group cam disposed in the cam cylinder 108 following the rotation of the cam cylinder 108. Similarly, the second group lens-barrel 111 is controlled so as to straight move by another cut-out formed in the linear movement cylinder 109 in parallel with the optical axis and fitted with the second-group cam follower so that the second group lens-barrel 111 moves back and forth without rotation along the second group cam disposed in the cam cylinder 108 following the rotation of the cam cylinder 108. Thereby, the first group lens-barrel 110 and the second group lens-barrel 111 are movable at positions for shooting. The lateral sectional view in FIG. 9 shows the positional arrangement of the conventional lens barrel, wherein the focal length is variable by appropriately changing the space between the first group lens 104 and the second group lens 105 with the cam of the cam cylinder 108.
A lens barrier 110a is for protecting lenses of the lens barrel in the storing mode; a barrier base board 110b includes a sliding surface of the lens barrier 110a; a barrier cap 10c is for preventing the lens barrier 110a from dropping off and for forming a movement space of the lens barrier 110a with the barrier base board 10b and the barrier cap 10c; and a barrier drive ring 10d is for closing the lens barrier 110a. 
A third group lens-barrel 112 retains the third group lens 106 having a focusing function so as to move the third group lens-barrel 112 in an optical axial direction for focusing. A guide bar 113 is for supporting the third group lens-barrel 112 movably along the optical axis, and is studded in the CCD base board 102; a motor 114 for driving the third group lens-barrel 112 is fixed to the CCD base board 102; a screw 114a is rotated by the motor 114; a bearing 115a is for journaling the guide bar 113; and a bearing 115b is for journaling the screw 114a. Both the bearings 115a and 115b are fixed to the CCD base board 102. The third group lens-barrel 112 is provided with a nut screwed to the screw 114a and fixed not to be rotated, so that the third group lens-barrel 112 is back-and-forth driven by the motor 114, enabling focusing operation.
In a state that a signal produced from an image picking-up unit is not used for shooting, there may be a case where the entire lens-barrel length is reduced for improving the portability and reducing the storage space of an image picking-up apparatus. Therefore, in a collapsed mode of the lens-barrel, as shown in FIG. 8, the second group lens-barrel 111 may be stored so as to enter the movable range of the third group lens-barrel 112. In such a structure, in order to avoid components for moving the third group lens-barrel 112, such as the guide bar 113, the screw 114a, and their bearings 115a and 115b, the second group lens-barrel 111 must be largely cut out.
FIG. 10 is a front view of the second group lens-barrel 111, wherein reference numeral 116 denotes regions cut out of the second group lens-barrel 111 for avoiding the bearings 115a and 115b of the guide bar 113 and the screw 114a, and a bearing (not shown) for journaling a bar for suppressing the rotation of the third group lens-barrel 112 about the guide bar 113. Numeral 117 denotes regions cut out for avoiding the first group cam follower, three of which are arranged substantially at the same intervals. Numeral 118 denotes a cut-out region for driving the lens barrier for protecting lenses in a storing mode.
As described above, in the conventional second group lens-barrel 111, the area of the cut-out regions is so large that there have been problems of strength insufficiency and light leakage. The problem due to the strength insufficiency is instability in retaining lenses, leading to the deterioration of optical functions. The addition of ribs for ensuring a sufficient strength is against the miniaturization of the lens barrel, so that it is not meaningful to store the second group lens-barrel 111 so as to enter the movable range of the third group lens-barrel 112.
The light leakage is a phenomenon that light other than a luminous flux for shooting is picked up by the image picking-up means. In the conventional lens barrel, light entering the first group lens 104 at an angle and then reflected by the internal surface of the linear movement cylinder 109 may enter the CCD 101 without passing through the second group lens 105. However, since the second group lens-barrel 111 includes the large cut-out regions, such light leakage cannot be prevented, providing challenges to the miniaturization of the lens-barrel.